As is well known in the art, dispersions of visible light reflecting agents such as, for example, titanium dioxide, are generally added to aqueous alkaline solutions such as photographic processing compositions and to liquid organic media such as pigmented lacquers and plastic materials. It is known in the photographic art that titanium dioxide particles, due to their highly effective reflection properties, may be used to appreciably lessen or eliminate undesirable effects such as, for example, fogging. Likewise, in the paint industry, it is known to use a dispersion of titanium dioxide to influence the properties of the products in regard to hue, gloss and physical and chemical behavior.
Importantly, to realize the beneficial effects described above, the titanium dioxide particles comprising the dispersion must remain substantially dispersed, i.e., uniformly distributed, in the aqueous alkaline solutions or in the liquid organic media to which they are added.
U.S. Pat. 3,642,510 describes a process for preparing titanium oxide pigments which are dispersable in hydrophobic systems such as paints or varnishes by adding an alkali metal salt of a high molecular weight carboxyl compound to a titanium oxide slurry finely dispersed in water or an alcohol containing an aluminum salt or zinc salt to form a soap of aluminum or zinc on the surface of the titanium oxide.
U.S. Pat. 4,235,768 describes a process of coating a titanium dioxide pigment with an organic polymer containing carboxyl groups to produce a homogeneous dispersion of the pigment in liquid organic media, e.g., pigmented lacquers and plastic materials.
U.S. Pat. 4,246,040 describes a method of surface treating a powdery or granular solid substance such as titanium dioxide which comprises reacting a basic polyaluminum salt with an acid or its salt in the presence of the titanium dioxide to alter the hydrophilic or lipophilic properties of the titanium dioxide.
Methods are known in the art to alleviate or circumvent the undesirable results brought about by the settling, agglomeration and/or random adhesion of titanium dioxide particles in aqueous alkaline processing compositions, for example, by encapsulating the titanium dioxide particles such as disclosed in U.S. Pat. 3,833,369; or, by adding additional titanium dioxide particles to the processing composition, so that, in effect, the settling out of the titanium dioxide particles still occurs but the amount present overall provides suitable reflection.
As would be understood by those of skill in the relevant art, efforts to eliminate the settling of titanium dioxide particles in aqueous alkaline processing compositions can be difficult without detrimentally affecting the photographic quality of diffusion transfer film units. In other words, due to the complexity of the chemical interactions between the constituents of the processing composition, as well as, the interactions of the processing composition with the other components of the film unit, minor changes in the formulation of the processing composition can have a significant impact on the resulting photographic product.
As the state of the art advances, novel approaches continue to be sought in order to attain the required performance criteria for the systems described above. There is a need for novel photographic processing compositions that have advantages over those already known to the art; therefore, investigations continue to be pursued to provide such advantages.
It is therefore an object of this invention to provide a novel photographic processing composition for use in photographic diffusion transfer film units and processes.
It is another object of the present invention to provide diffusion transfer photographic film units and processes which include the novel processing compositions.